This invention concern liquid leak detection methods and more particularly leak detection using dyes which fluoresce when illuminated by light of particular wavelengths, typically ultraviolet light, commonly referred to as xe2x80x9cblack lightxe2x80x9d.
Ultraviolet light sources are commonly employed for such uses as disinfection, prospecting, document examination, dental work curing, as well as leak detection.
The fluorescing dye is typically mixed with lubricating oil which in turn is mixed with fluid in the equipment being inspected, such as in the refrigerant of an air conditioning system.
If a leak is present, the dye in the fluid leaked out will fluoresce when illuminated with ultraviolet light, so that the leaked fluid will be readily visible.
Such dyes will fluoresce or emit light at certain visible band wavelengths, when excited by shorter wavelength ultraviolet light.
In order to make such leak detection easy and reliable, particularly under bright light ambient conditions, a powerful light source emitting light at the proper wavelength should desirably be used, which source does not also emit visible light. If visible light is reflected from the surface being inspected, it will render the fluorescing light less conspicuous.
Currently available light sources are not of sufficient intensity and also emit significant visible wavelengths such that the contrast of the fluorescent light with the visible reflected light is not great enough for reliable observation.
An overheating problem is also encountered in attempting to eliminate visible light by absorption in a filter lens.
This overheating can crack or shatter the lens, particularly if water drops impinge on the lens, the shattered glass presenting a hazard to the user.
In attempting to create a more powerful light source, reflectors are commonly provided which concentrate and direct ultraviolet wavelength light emitted from a quartz envelope lamps. Prior art reflectors have typically been crudely formed and had low efficiency due to destruction interference set up by protective coatings such as silicon dioxide.
It is the object of the present invention to provide a system for ultraviolet light illumination of enhanced intensity for fluorescent leak detection to allow easier and more reliable viewing of fluorescent light emitted from a dye.
It is another object of the present invention to provide an ultraviolet light source which emits an intense ultraviolet beam directed through a glass filter so as to eliminate visible wavelengths but without producing heating of the glass filter.
The above objects and others which will become apparent upon a reading of the following specification and claims are achieved by a system comprised of an improved parabolic reflector and filter associated with an ultraviolet lamp, combined with viewing eyeglasses which filter certain visible wavelengths for achieving maximum contrast of the fluorescing light emitted from a dye exposed to the illumination by a leak.
The improved reflector has an accurately formed parabolic shape. Two coatings of precisely control thickness are applied to the reflecting surface and each have a substantially different refraction indices. These coatings minimize the interference of a reflected ultraviolet light beam with the incident light beam by inducing offsetting phase shifts such that the reflected light is closely in phase with the incident light. This result maximizes the intensity of the reflected ultraviolet light beam by minimizing destructive interference between the incident and reflected light beams which could otherwise occur. The ultraviolet light source is preferably a quartz envelop tungsten halogen lamp mounted at the focal point of the reflector parabola.
The ultraviolet light beam from the reflection is then passed through an optical filter to selectively remove visible light from the reflected light beam by a process of selective reflectance rather than absorbance so as to minimize heat build up in the filter, as has occurred in previous light absorbing filters used for removing visible light.
A series of coatings are applied to a borosilicate glass disc in order to achieve this. Successive coating layers of high and low refraction indices are used to produce selective reflectance of a wavelength band above the ultraviolet wavelengths but shorter than the infrared band, i.e., from 475 nm to 700 nm.
The infrared light is transmitted through the filter to reduce heating of the confined space behind the filter.
The final element of the system is a pair of filtering viewing eyeglasses which absorb wavelengths just below the wavelength of the fluorescing light in order to block wavelengths of the illuminating light in this band, to increase the contrast and visibility of the fluorescence of the illuminated dye to the viewer""s eye.
The overall result is to produce an intense beam of ultraviolet light containing minimal visible wavelength light using practical components. The fluorescent light is thus strong and is not masked by the incidence of reflected visible light from the illuminating beam.